1. Field of the Invention
The invention generally relates to limiting amplifiers and in particular to limiting amplifiers for optical communication.
2. Description of the Related Art
High speed limiting amplifiers (LA) play a critical role in various wireline communications, amplifying a weak signal to deliver a large output swing for succeeding data recovery circuit. FIG. 1 shows a conventional wireline communication system, where laser 12, driven by driver/modulator 14 outputs an optical signal to a receiver through optical fiber 15. Photo diode 16 detects the optical signal to generate a weak current signal, which is then transformed by transimpedance amplifier (TIA) 18 to a voltage signal, usually with a swing of only several or tens of mV. The weakness of the voltage signal from TIA 18 necessitates limiting amplifier 20 to amplify the voltage signal such that a signal with a full swing can be provided to clock and data recovery circuit (CDR) 22 to achieve high speed digital data processes. Limiting amplifier 20 may precede or follow an optional equalizer (not shown).
Conventional Cherry-Hopper amplifiers have been employed in limiting amplifiers to achieve a data rate of 40 Gb/s in heterojunction bipolar technology, but the power dissipation is prohibitive. Possible solutions in CMOS technology are to use a wideband amplifier with inductive peaking and a distributed amplifier (DA) or a cascaded distributed amplifier (CDA). The bandwidth of a DA is good, but the gain is low. It is desired to have a limiting amplifier with low power consumption, a high gain and greater bandwidth.